Car Care

The importance of choosing the right fuel for your car

We are all starting to feel the squeeze at the pump from the recent hike in petrol prices.

With our regular 91 octane now exceeding the $3 dollar mark, it can be tempting for motorists to choose the cheaper option. However, it is extremely important to fill your car up with the octane type your owner's manual recommends.

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Understanding different fuels is very important, using the wrong type of fuel in your car can be catastrophic for the engine. A lot of testing and quality control goes into creating the best blend of fuel to suit your car. While most modern engines can adapt themselves to safely run on most octane levels, engines are optimised to use the fuel recommended by the manufacturer.

What can happen when we put the wrong fuel type in the tank?

Inside an engine, a petrol/air mixture is compressed by a piston, ignited by a spark, with the resulting explosion pushing the piston down. If the petrol detonates too early, which can happen when using a lower octane fuel than the engine needs, it can try to force the piston down before it has reached the top of its stroke. This is noticeable as a ‘knocking’ sound in your engine and can cause major damage if left unchecked.

Detonation can cause major internal failure including…

  • Melted spark plug electrodes
  • Cracked piston rings
  • Melted or cracked pistons
  • Hammered rod bearings
  • Blown head gaskets

Can you use any grade of petrol in a car?

The octane rating of petrol - 91, 95 or 98 in New Zealand - signifies its ability to resist detonation.

An engine is tuned to use petrol of a certain octane, and the higher the octane number, the more compression the fuel can withstand before detonating. Put simply, the fuel will burn at a different rate.

So, if your car requires 91 octane then that’s all you need, but you can use 95 or 98 octane petrol if you’re happy to pay more. If your car requires 95 octane you must use 95 or 98, but not 91. The bottom line is to use the recommended octane as a minimum.

Are the types of fuels sold by various brands different?

Vladimir Koutsaenko, Senior Advisor - Fuel Quality Monitoring from Trading Standards (which is part of the Ministry of Business Innovation and Employment) says there’s not much difference.

“The sampling and testing we undertake helps ensure that all fuels sold are in line with legal specifications. Some motorists are convinced that their car performs better on one brand of fuel than another. This is hard to prove or disprove.

“Fuels sold in New Zealand are well suited for a variety of vehicles. Road and traffic conditions, along with other factors such as how a vehicle is being driven will have major effects on fuel consumption and performance.

“If fuels are advertised as having properties that make them superior, they must conform with the specifications when tested. If you are not sure if a fuel is suitable for your vehicle – such as ethanol-blended petrol, which could be damaging to very old cars' components – we recommend checking the owner’s manual or contacting the manufacturer’s local agent.”

Why is fuel so expensive?

Automobile Association Principal Adviser Terry Collins says the Omicron outbreak, import costs and supply problems were also contributing to higher prices.

Another factor is that with European nations breaking ties with Russia, they will be forced to source their fuel from the same markets as New Zealand or its oil. This in turn means prices will continue to steadily increase.

In an unprecedented move the Government announced that from 11.59 pm Monday 14 March 2022 there would be a temporary reduction in the fuel excise tax by 25 cents per litre for three months. The 25-cent cut is on the fuel excise duty, it is not on the GST. It’s expected the tax cuts will save Kiwi motorists between $11 and $17 for a full tank.

The temporary reduction in fuel excise tax has been introduced as part of a cost-of-living package - aimed at giving New Zealand families immediate relief through the current global energy crisis triggered by the war in Ukraine.


Is New Zealand’s fuel quality better or worse than in other countries?

Our fuel quality specifications are in line with those in similar economies like Australia, the USA, and the UK.

Koutsaenko says, “There is a Worldwide Fuel Charter which sets out car manufacturer expectations and requirements for fuels, to help ensure compatibility with the vehicles produced. Fuel specifications are periodically updated, reflecting developments with motor vehicle technology in response to environmental and health requirements.”

So, if you are tempted to save money at the pump by opting for the lower cost 91 octane fuel option - The answer to that is a big - no, you won’t save money. As it may even end up costing you more money in the long run.

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